The Absorption Spectrum of the Lowest Triplet State in Crystalline trans-Stilbene

The absorption spectrum of the lowest triplet state (T₁*-S₀) of trans-stilbene is observed between 14,000 and 18,000 cm^?1 with a crystal four centimeters long, cooled to 4.2°.K. This transition is more intense (f=3×10^?9) than the similar transition in anthracene, due to vibration-induced spin-orbital coupling. Vibrational structures in the spectrum are well resolved and seven frequencies are assigned to normal modes in the T₁* state of trans-stilbene. Exciton structures in crystal are not resolved.